People from the Ryukyu Islands (of which Okinawa is the largest) have a life expectancy among the highest in the world,[2] although the male life expectancy rank among Japanese prefectures has plummeted in recent years.[3]

The traditional diet of the islanders contains 30% green and yellow vegetables. Although the traditional Japanese diet usually includes large quantities of rice, the traditional Okinawa diet consists of smaller quantities of rice; instead the staple is the purple-fleshed Okinawan sweet potato. The Okinawan diet has only 30% of the sugar and 15% of the grains of the average Japanese dietary intake.[4]

The traditional diet also includes a tiny amount of fish (less than half a serving per day) and more in the way of soy and other legumes (6% of total caloric intake). Pork is highly valued, and every part of the pig is eaten, including internal organs. However, pork is primarily only eaten at monthly festivals[4] and the daily diet is almost entirely plant based.[5]

Between a sample from Okinawa where life expectancies at birth and 65 were the longest in Japan, and a sample from Akita Prefecture where the life expectancies were much shorter, intakes of calcium, Iron and vitamins A, B1, B2, C, and the proportion of energy from proteins and fats were significantly higher in Okinawa than in Akita. And intakes of carbohydrates and salt were lower in Okinawa than in Akita.[6]

The quantity of pork consumption per person a year in Okinawa is larger than that of the Japanese national average. For example, the quantity of pork consumption per person a year in Okinawa in 1979 was 7.9 kg (17 lb) which exceeded by about 50% that of the Japanese national average.[7]

An Okinawan reaching 100 years of age has typically had a diet consistently averaging about one calorie per gram of food and has a BMI of 20.4 in early adulthood and middle age[citation needed]

In addition to their high life expectancy, islanders are noted for their low mortality from cardiovascular disease and certain types of cancers. Wilcox (2007) compared age-adjusted mortality of Okinawans versus Americans and found that, during 1995, an average Okinawan was 8 times less likely to die from coronary heart disease, 7 times less likely to die from prostate cancer, 6.5 times less likely to die from breast cancer, and 2.5 times less likely to die from colon cancer than an average American of the same age.[4]

The traditional Okinawan diet as described above was widely practiced on the islands until about the 1960s. Since then, dietary practices have been shifting towards Western and Japanese patterns, with fat intake rising from about 10% to 27% of total caloric intake and the sweet potato being supplanted with rice and bread.[8]

The diet consists of a relatively high energy intake, and contains similar foods to the traditional Okinawan diet. The principal focus of the diet consists of knowing the food energy density of each food item.

The proponents of this diet divide food into four categories based on caloric density. The "featherweight" foods, less than or equal to 0.8 calories per gram (3.3 kJ/g) which one can eat freely without major concern, the "lightweight" foods with a caloric density from 0.8 to 1.5 calories per gram which one should eat in moderation, the "middleweight" foods with a caloric density from 1.5 to 3.0 calories per gram which one should eat only while carefully monitoring portion size and the "heavyweight" foods from 3 to 9 calories per gram which one should eat only sparingly.[9]